Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Heart valve – Having rigid or semirigid pivoting occluder
Reexamination Certificate
2000-12-14
2003-11-11
Willse, David H. (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Heart valve
Having rigid or semirigid pivoting occluder
Reexamination Certificate
active
06645244
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to prosthetic mechanical heart valves and in particular, to a bi-leaflet mechanical valve with an improved pivoting mechanism.
BACKGROUND OF THE INVENTION
During each cardiac cycle, the natural heart valves selectively open to allow blood to flow through them and then close to block blood flow. During systole, the mitral and tricuspid valves close to prevent reverse blood flow from the ventricles to the atria. At the same time, the aortic and pulmonary valves open to allow blood flow into the aorta and pulmonary arteries. Conversely, during diastole, the aortic and pulmonary valves close to prevent reverse blood flow from the aorta and pulmonary arteries into the ventricles, and the mitral and tricuspid valves open to allow blood flow into the ventricles. The cardiac valves open and close passively in response to blood pressure changes operating against the valve leaflet structure. Their valve leaflets close when forward pressure gradient reverses and urges blood flow backward and open when forward pressure gradient urges blood flow forward.
In certain individuals, the performance of a natural heart valve is compromised due to a birth defect or becomes compromised due to various disease processes. Surgical repair or replacement of the natural heart valve is considered when the natural heart valve is impaired to an extent such that normal cardiac function cannot be maintained. The natural heart valve can be replaced by homograft valves obtained from the same species (e.g., human donor heart valves), heterograft valves acquired from different species, and prosthetic mechanical heart valves.
The present invention is directed to improvements in prosthetic mechanical heart valves. Modern implantable mechanical heart valves are typically formed of a relatively rigid, generally annular valve body defining a blood flow orifice and an annular valve seat and one or more occluders that are movable between a closed, seated position in the annular valve seat and an open position at an angle to the valve body axis. These components of mechanical heart valves are made of blood compatible, non-thrombogenic materials, i.e., pyrolytic carbon and titanium. A bio-compatible, fabric sewing ring is typically provided around the exterior of the valve body to provide an attachment site for suturing the valve prosthesis into a prepared valve annulus. The occluder(s) is retained and a prescribed range of motion is defined by a cooperating hinge mechanism or other restraining mechanism. Such prosthetic heart valves function essentially as check valves in which the occluder(s) responds to changes in the relative blood pressure in the forward and reverse directions as described above and move between their open and closed positions.
A wide variety of mechanical heart valve designs have been proposed and/or utilized in the past. For example, an early clinically used mechanical heart valve employed a spherical ball moving into and out of engagement with an annular seat within a cage in response to the normal pumping action of the heart. Other clinically used heart valve prostheses have employed occluders in the form of a circular disc that pivots open and closed in response to blood pressure changes while being restrained by cooperative structure of the valve body.
A further clinically used bi-leaflet heart valve prosthesis employs a pair of semi-circular or semi-elliptical plates or leaflets that hinge open and closed together. Such bi-leaflet heart valves are typically entirely formed with a pyrolytic carbon or with pyrolytic carbon coating on all exterior surfaces of the valve body and leaflets. A typical method of coating pyrolytic carbon onto a valve substrate is disclosed in U.S. Pat. No. 3,526,005. The pyrolytic carbon coating provides wear resistant surface, and provides insurance against thrombus formation on such surfaces.
Bi-leaflet heart valves generally utilize pivot or hinge mechanisms to guide and control the motion of the leaflets between the seated, closed position and the open position. In such design configurations, two mirror image leaflets are typically disposed in opposed or mirror image relation to one another. Upon closure, each valve leaflet occludes or covers half of the annular valve orifice or valve annulus. Generally, each leaflet is designed with roughly semicircular shape and has a rounded exterior margin and peripheral edge which engages an inner seat surface of the valve body to provide a peripheral seal, and an inner, diametrically extending edge and adjacent margins adapted to abut against the counterpart edges and margins on the other leaflet. Each leaflet can rotate about an axis defined by a pair of opposed hinge pivot points in opposed hinge recesses that are offset from the central axis of the valve annulus. The leaflets are typically flat, but curved or elliptical leaflets have been proposed.
Such mechanical heart valves are typically designed in somewhat differing profile configurations for replacement of differing impaired natural heart valves. However, the basic in vivo operating principle is similar regardless of configuration. Using an aortic valve as an example, when blood pressure rises in response to left ventricle contraction or systole in each cardiac cycle, the leaflets of such a valve pivot from a closed position to an open position to permit blood flow past the leaflets. When the left ventricle contraction is complete, blood tends to flow in the opposite direction in diastole in response to the back pressure. The back pressure causes the aortic valve leaflets to close in order to maintain arterial pressure in the arterial system.
The most widely accepted type of bi-leaflet heart valve presently used mounts its leaflets for pivoting movement by means of a pair of rounded ears extending radially outwardly from opposed edges of the leaflets to fit within rounded hinge recesses in opposed flat surfaces of the valve body side wall. Such bi-leaflet valves are exemplified by the mitral valve depicted in U.S. Pat. No. 4,276,658 and the aortic heart valve depicted in U.S. Pat. No. 5,178,632, both incorporated herein by reference.
The leaflet ears are received within curved hinge recesses extending radially into opposed flat surfaces of thickened wall sections inside the annulus of the generally cylindrical or annular valve body. Each hinge recess is designed in at least one respect to match the shape of the leaflet ear and is bounded by sets of leaflet stop surfaces angled to define the extreme open and closed leaflet positions. In other words, where the ear is formed as a portion of a circle having a given radius, the counterpart hinge recess is formed as a semicircle having a slightly greater radius. An inverse arrangement of the ear and recess hinge mechanism is depicted in U.S. Pat. No. 5,354,330, incorporated herein by reference, whereby the leaflet ear is replaced by a leaflet recess, and the hinge recess is replaced by a complementary shaped hinge boss.
To achieve the pivoting mechanism, the mating surfaces of the ears and recesses are precisely machined so as to provide a small but definite working clearance for the ears to pivot about the necked down pivot surface and be retained within the hinge recesses. During valve assembly, the annular valve body is deformed or distended so that the leaflet ears may be inserted into the respective hinge recesses. Each manufactured heart valve is then lab tested “dry” to ensure that the leaflets are held tightly enough to be secure against falling out of their hinge recesses, but are not so tightly engaged so as to create a binding or restricted valve action.
The range of leaflet motion is typically controlled by pins or ramps or opposed side stops of the hinge recesses or by hinge bosses in the valve body. In one format described in the above-incorporated '632 patent, the hinge recess is generally spherical and bounded by open and closed stop surfaces of a stop member projecting into the recess. In the other formats depicted in the above-incorporated, &apos
Gross Jeffrey M.
Shim Hong S.
Shu Mark C.
Berry Thomas G.
Latham Daniel W.
Matthews Williams H
Medtronic Inc.
Willse David H.
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